70 Prof. Thury on the Law of the Production 
It is plain that, according to the author, the life of the un- 
fecundated ovum is divisible into two periods. In the first of 
these it is in principle a female ovum, in the second a male 
ovum. The turning moment (moment de vire), according to the 
author, is the time (probably very short) which separates the 
two periods, and in which the natural course of development 
induces some sudden change, the nature of which histology 
should reveal to us. He assumes that the relative duration of 
the two periods of the life of the ovum may be modified under 
the influence of the organic state of the female, whence would 
result a predisposition on the part of some females to give birth 
either to individuals of their own sex or to males. Temperature, 
by its direct action upon the ovum, and the influence of the 
fecundating male upon the organic condition of the female, 
would also produce similar results. 
The author, in all his deductions, appears to start from a 
general point of view, which he certainly indicates, but nowhere 
demonstrates in a positive manner, regarding it apparently as a 
sort of axiom. He assumes that “ sexual life, being common to 
animals and plants, must be subjected to identical fundamental laws 
in both kingdoms.” If this be true of the two kingdoms, it must 
apply with still more reason to the various divisions of the same 
kingdom. This admits of much generalization ; but (and this is 
the difficulty) we have yet to distinguish with certainty the facts 
which bear upon essential laws from the infinitely varied mani- 
festations by which these same laws are realized in combination. 
The second and third parts of M. Thury’s memoir are here 
reproduced entire. 
Second Part. Summary and Practical Observations. 
1. Sex depends on the degree of maturation of the ovum at 
the moment of its fecundation. 
2. The ovum which has not attained a certain degree of ma- 
turation, if it be fecundated, produces a female; when this de- 
gree of maturation is passed, the ovum, if fecundated, produces 
a male. 
3. When, at the rutting-season, a single ovum separates from 
the ovary to descend slowly through the genital canal (as in uni- 
parous animals), it is sufficient that the fecundation takes place 
at the commencement of the rutting-season to produce females, 
and at the end to produce males—the turning-point of the ovam. 
occurring normally during its passage in the genital canal. 
4, When several ova separate successively from the ovary 
during a single generative period (multiparous animals and ovi- 
parous animals in general), the first ova are generally the least 
developed, and produce females ; the last are more matyre, and 
